These days, control elements and display devices as well as buttons of all types are incorporated in automobile interiors in recesses in a large panel. This results in gaps and material transitions.
Currently known solutions may be summarized as follows:
Membrane keyboards with embossing or coating application: membrane keyboards meet the requirements of a continuous surface and, through embossing or selective coating or silicone application, of formed-on button geometries, are however always restricted to a flat basic geometry. See for example DE 20 2005 012 021 U1.
Thermoformed film: as a result of thermoforming, films may be transformed into a three-dimensional shape and button geometries may also be formed. Limitations result from the required bending radii (sharp edges are impossible) and the minimum spacing of the buttons (there must be sufficient material for thermoforming between the buttons). Functional actuation of such a button is also not simple to achieve, since the deformed film also has to effect the button stroke. Such films also have a great tendency to fail quickly during an actuation endurance test.
Silicone surface: freely shaped functional operator interfaces may be made from silicone. This solution is distinguished by a soft surface and limited brilliance of the silicone colours. It is for this reason that this solution is often not selected precisely for large-area applications.